1. Field of the Invention
The present invention relates to air intake manifolds for fuel-injected internal combustion engines, particularly for motor vehicles.
The invention relates more specifically to an intake manifold of this kind, of the type comprising, for each combustion chamber of the engine, an air duct, a downstream part of which comprises a single length of tube connected to at least one flange for attaching to the cylinder head of the engine, and an upstream part of which comprises two lengths of tube, namely a short upstream length and a long upstream length, each of which is fed with air via its upstream inlet from means of controlling the flow rate of inlet air, such as a throttle body, the downstream outlet of each length of upstream tube being intended to be placed in communication with the upstream inlet of the single length of downstream tube.
2. Description of the Prior Art
For noise-emission reasons, and for each air duct, it is known practice for the injector holder, which is made in the form of a small-size and lightweight element in an intake manifold, to be connected to the other elements of this manifold by a flexible sleeve, fixed to the engine block by at least one vibration damper, generally of the type known as a "silentbloc".
For such an intake manifold to exhibit, in response to the various running speeds of the engine, an acoustic law which is favorable to good filling of the engine, that is to say to the transfer to the engine of the column of air drawn in with minimum impedance, it is known practice for the manifold to be given a variable geometry, more particularly by varying the lengths of the air ducts, each of which extends between a means of controlling the flow rate of the air supplied to the engine, such as a throttle body, and the engine cylinder head, for supplying a cylinder of this engine with air.
To achieve this, it is known practice for each air duct to comprise two tubes in parallel, or for its upstream part to comprise two lengths of tube in parallel which meet, continuing with a single downstream length of tube, in series in the downstream direction with the two upstream lengths of tube, and for a restriction member or flap to be mounted to pivot in one or other of the two tubes or in one of the two upstream lengths of tube, and controlled in such a way as to close this upstream tube or upstream length of tube to a greater or lesser extent according to the engine running speed, so that a variation equivalent to a variation in length and/or diameter of the air duct is obtained.
However, these known arrangements have the drawback that depending on the engine running speeds, only one of the upstream tubes or lengths of tube or both tubes or lengths of tube simultaneously has or have the air passing through it or them, but not one or the other, which means that the acoustic response of the air duct is not perfectly suited to the needs, because of parasitic resonance.
In order to overcome the aforementioned drawback of such variable-geometry intake manifolds, and produce an intake manifold that can extend the engine charge range over which the acoustic impedance of the manifold is the most favorable, EP-A-355 960 discloses an intake manifold of the type presented hereinabove, and in which the downstream outlet of each upstream length of tube is placed in communication with the upstream inlet of the single downstream length of tube via an element mounted between the upstream part and downstream part of each air duct, and through which there passes an acoustic bore, said element being able to move between two extreme positions, in one of which said element closes said short upstream length of tube while its acoustic bore connects said long upstream length of tube to said downstream length of tube, whereas in the other extreme position, said element closes said long upstream length of tube while its acoustic bore connects said short upstream length of tube to said downstream length of tube.
This manifold thus makes it possible to place one or other of the two upstream lengths of tube in series with the single downstream length of tube, the long upstream length of tube allowing the longest possible air duct to be obtained, suitable for low engine speeds because it is tuned to the low resonant frequencies, while the short upstream length of tube, in series with the single downstream length of tube, makes it possible to obtain the shortest possible air duct suitable for when the engine is running at high speeds, because it is tuned to high resonant frequencies.
This intake manifold thus produces an acoustic response which is better suited to the engine speed.
However, the moving element in EP-A-355 960 is a cylindrical rotary valve which rotates on itself about its axis by about one third of a revolution in order to move from one of the extreme positions to the other, something which is a disadvantage in terms of controlling it, and demands products with close tolerances, which are therefore expensive, if problems of sealing between the air ducts are to be avoided.
The problem underlying the invention is that of providing an intake manifold of the type known from EP-A-355 960, but which is better suited than those described in that document to the various requirements of practice, and in particular as far as the compactness, the simplicity and the economy of manufacture of the control of the moving part, the amount by which it moves and the means for sealing it are concerned.